Acid baths for cleaning and pickling metal



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United States Patent 0 ACID BATES FOR CLEANING AND PICKLING METAL AlbertJ. Saukaitis, Wayne, Pm, nssignor to Amchem Products, Inc., Ambler, Pa.,a corporation of Delaware No Drawing. Filed May 14, 1957, Ser. No.658,961

7 Claims. (Cl. 252-451) Xfi' This invention relates to the art ofcleaning and pickling metal surfaces and is particularly concerned withthe provision of a newmethod and bath for cleaning and pickling surfacesof mild steel, zinc (particularly galvanized steel) and aluminum.

As is well known to those skilled in the art, the cleaning and picklingof the metals mentioned is commonly effected by means of acid bathswhich remove scale or oxide from the surface and the principal object ofmy invention is to provide improved baths for this purpose.

The cleaning and pickling acids with which my invention is especiallyuseful are those non-oxidizing mineral acids from the class whichconsists of sulphuric, phosphoric, hydrochloric, r ilfamic, hydrollub'fic and fluosll sisa My invention resides in the discovery that theaddition of a small amount of triphenyl sulfonium chloride to anslsanias 9 1PiFEQPQQhlE QEPfgl iglfi describsd substantialj prevents orretards the attack of the acid on the Basis metalwithoutinterfefing withtheremovahof scale or x15513651 the surface? carrying out my inventionthe baths are normally used at conventional concentrations of acid andat customary temperatures. These factors, therefore, are familiar to theart and can be varied as desired within the practices which arecustomary in this field.

The quantity of triphenyl sulfonium chloride which I incorporate in suchbaths can vary but should, of course, be suflicieut to substantiallyreduce the rate of acid attack on the basis metal while stillaccomplishing the "desired 'cleaning and pickling. In general, only arelatively small amount of triphenyl sulfonium chloride is required andmy experience indicates that this need be np greater than approximately1% by weight of the bath, although this limit may be exceeded to areasonable extent without, apparently, in any way impairing the desiredresults. As a practical matter, a useful amount for any particular acidor type of work can easily be determined by simple test within theknowledge of those skilled in this art.

By way of specific examples the following may be noted but they are inno sense to be considered as limiting. Certain commercial picklingprocedures involve use of a 10% 66 B. sulfuric acidbath heated toapproximately 180 F. Aba'sic bath of this kind was prepared and to aportion of it was added A triphenyl sulfonium chloride. A succession ofmild steel panels were then pickled in the bath for .6 hour each. Panelstreated after the 1st, 3rd, th, 22nd, 24th, 26th and 28th hours of bathlife were weighed before and after pickling and the weight lossrecorded. These weight losses were respectively: 0.615, 0.665, 0.72,0.75, 0.81, 0.748, and 0.764 gram per square foot per 36 hour immersion.The basic bath containing no inhibitor when used on identical steelpanels caused a 72.5 gram per square foot weight loss per 16 hourimmersion. The data, therefore, clearly illustrates "ice Patented June21, 1960 2 the value of my invention in inhibiting attack of the bathupon the metal and further demonstrates that iron buildup in the bathdoes not materially impair the efiiciency of the inhibitor.

In another example a 3% sulfamic acid olution em ploying 36% by weightof triphenyl sulfonium chloride was used to pickle a galvanized steelpanel. After remaining in the solution for 64 hours, the panel showedmuch less nos'in than an exactly similar panel pickled in the same '5 ofacid solution but containing a familiar commercial inhibitor espectiallyrecommended for use in the pickling of galvanized steel instead of thetriphenyl sulfonium chloride of my invention. This was true even whenthe panel was left in the solution for as short a time as 2 hoursinstead of the 64 hours for the panel treated with the bath of myinvention.

In connection with sulfamic acid baths, I should like to point out thatthese are quite widely used in the cleaning of aluminum, particularlyaluminum which is employed in the handling of milk. Such aluminum milkhandling equipment frequently becomes completely encrusted with milkscale and it is customary to employ sulfamic acid to remove such scalebut, unfortunately, this acid also seriously attacks the aluminum.However, a cleaning solution consisting of grams of sulfamic acid withsufficient water to make cc. when inhibited with A gram triphenylsulfonium chloride satisfactorily cleaned a severely encrusted aluminumvessel without substantial attack on the basis metal. This, therefore,constitutes a preferred embodiment of my invention.

Still another example involved steel panels certain of which wereimmersed in a 75% phosphoric acid pickling solution containing 1%triphenyl sulfonium chloride. The bath was employed at 45 C., and thepanels lost only 1.17 grams per square foot after 24 hours immersion,whereas, similar panels pickled in a similar but uninhibited phosphoricacid solution lost 209 grams per square foot after only 17.5 hours ofimmersion.

In conclusion, cleaning and pickling of metals according to my inventioncan be carried out with any of the procedures familiar in this art as bycontinuously passing the metal to be pickled (such as wire or sheets)through a nhmber of baths in a regulated manner or by immersing thearticles in the bath for a suitable period of time. The temperature maybe varied as indicated above, but ordinarily the baths of my inventionare used at temperatures of from to F.

I claim:

1. A mineral acid bath for cleaning and pickling metal surfaces, saidbath containing, as an inhibiting addition agent, an amount of triphenylsulfonium chloride which is sufficient to reduce the rate of acid attackon metal.

2, The method of cleaning and pickling surfaces of dteelfzinc andaluminum which consists in subjecting the surface to the 'catiou of abath according to claim 1.

3. A bath of claim 1 wherein the quantity of triphenyl sulfoniumchloride does not exceed 1% by weight of the bath.

4. The method of cleaning and pickling surfaces of steel, zinc andaluminum which consists in subjecting the surface to the action of abath according to claim 3.

5. An acid bath for cleaning and pickling metal surfaces, said bathcomprising acid from the class consisting of sulphuric, phosphoric,hydrochloric, sulfamic, hydrofluoric and fluosilicic acids and includingtriphenyl sulfonium chloride in an amount sufiicient to reduce the rateof attack of the acid on the metal.

6. The acid bath of claim 5 in which the mineral acid is sulfamic acid.

7. The method of cleaning and pickling surface? of steel, zinc andaluminum which consists in subjecting the surface to the action of abath according to claim 5.

References Cited in the file of this patent UNITED STATES pATgNTs SemonZ2 C./ 2/JJSApr. 5, 1932 Grebe et a1. -ZILCLifASept. 13, 1932 MacArthurct 9132;!!5.-- June 25, 1935 Arveson 2.s&: 2s 1=eb. 21, 1939 Lieber etaLZDZLAi-LH Mar. 7, 1939 Werntz "2.4141174 Oct. 31, 1939 4 Hunt -..e2f3:f Nov. 5, 1940 Jordon ..ZZC.:! Z Nov. 28, 1950 Hauser .2 C ..If:-Z Nov.2a, 1950 Skinner ..2' ::z? June 15, 1954 Meyer "252.1252- Jan. 4, 1955Funderburk et 1111 224222: Feb. 15, 1955 Cardwell =1 al.2.e:./ 7flf2Iu1y 12, 1955 Chiddix et a]. ffiizfl Aug. 21, 1956 Pitt -1291 4551321111 1 30, 1957 Beiswanger et 9.1.?211221. Nov. 26, 1957

1. A MINERAL ACID BATH OF CLEANING AND PICKING METAL SURFACES, SAID BATH CONTAINING, AS AN INHIBITING ADDITION AGENT, AN AMOUNT OF TRIPHENYL SULFONIUM CHLORIDE WHICH IS SUFFICIENT TO REDUCE THE RATE OF ACID ATTACK ON METAL. 